The present invention relates generally to liquid crystal displays. More specifically, this invention relates to a liquid crystal display in which analog information may be presented in other than alphanumeric manner and the interfacing by which the display is controlled is greatly minimized or eliminated.
As is well known, liquid crystal displays are electrically controlled devices utilizing the optical properties of liquid crystal materials to display desired patterns with only ambient light. Most commercial liquid crystal displays, and all of the so called "light-shutter" type liquid crystal displays discussed hereinafter, employ liquid crystal materials having a twisted nematic molecular orientation in the absence of an electric field. Such displays utilize principally one of two basic mechanisms by which light passing therethrough is controlled. In "field-effect" cells the presence of an electric field changes the direction of the liquid crystal material's optic axis. In "scattering" cells the presence of an electric field results in either intense light scattering due to a disruption in the ordered, unenergized molecular structure ("dynamic scattering") or an intense light focusing due to an ordering of the unordered, unenergized molecular structure ("quiescent scattering"). As a result of greater power requirements and slower response time of scattering cells, field-effect cells are greatly preferred in nearly all present day applications.
Presently nearly all liquid crystal displays are utilized to form fixed format, alphanumeric patterns. These displays are digital in nature, having a plurality of physically and electrically discrete, separately addressed, pattern segments. Such patterns require multiple-lead interfacing with generally costly, complex and physically large driving networks in order to effectuate the desired characters.
Perhaps the best known example of alphanumeric liquid crystal displays are those of the field-effect, light-shutter type in which a layer of nematic liquid crystal material is sandwiched between transparent parallel plates. A 90.degree. twist is induced in the nematic liquid crystal material by rubbing the plates at right angles to each other. Polarizers are placed adjacent to the outer surface of both plates such that when an electric field of sufficient potential is impressed across transparent conducting films applied to the inner surfaces of both plates, the nematic structure will untwist and the display will change from a light transmitting to an opaque medium or vice versa, depending upon the orientation of the two polarizers, thereby producing the aforesaid light-shutter effect. Typically the front plate conducting film is constructed with a plurality of physically and electrically separate conducting regions which, when appropriately, selectively energized, leave other regions unaffected so as to produce the desired letter or numeral.
Although some field-effect cells have attempted to display images or symbols other than letters or numerals, such liquid crystal displays have without exception required driving networks to appropriately control what quickly becomes a phenomenal number of separate conducting regions. Moreover, the greatly increased complexity of these networks over those associated with conventional alphanumeric display patterns has resulted in costly display controls frequently too large for most applications.
In much the same manner, the less desirable "scattering" type cells have also been utilized to form alphanumeric patterns. I am aware of only one instance in which general images or symbols other than letters or numerals have been formed with "scattering" type cells. In an article entitled "A Electronically Scanned Analog Liquid Crystal Display" published in Volume 9 Applied Optics, on pages 1323-1329 (June, 1970), the author, R. A. Soref, disclosed a technique for use with "scattering" type liquid crystal cells in which voltage gradients are induced transversely across the transparent conducting films so that the desired patterns can be formed. Although this technique does not require the use of the conventional driving networks previously noted, nevertheless driving equipment of a differeing type, including at least two voltage waveform generators external to the display, are required to effectuate even the simplest of patterns. The quantity of voltage generators, as well as the complexity of the voltage waveforms required, increases with the complexity of the desired pattern, likely resulting in an even more costly, complex, and a physically large display than needed for field-effect liquid crystal displays having similar patterns.